The present invention relates generally to an electric plug for an extension cord and, in particular, to a circuit breaker protected female electrical plug molded onto the end of a power cord.
Generally, when electrical appliances are connected to a typical wall receptacle, there is no overload protection in the power line against surges of electric current which might seriously damage the electrical appliances. Typically, the only safety devices provided are circuit interrupters which are adapted to either open or burn out when a current overload is present for a predetermined time.
Conventionally, the circuit interrupters are located centrally, particularly in a domestic establishment, with at least one circuit interrupter having a capacity of approximately 15 or 20 amperes governing each circuit. The amperage capacity of the circuit interrupter may be excessive and afford little protection for an individual electrical device. For example, a load with a critical power rating below such a capacity may be damaged or may create damage if its rating is exceeded for an appreciable length of time. The circuit interrupters fail to adequately protect appliances because a current overload which might be less than that required to open or burn out the interrupter, and still great enough to cause damage, can flow through the circuit interrupter unimpeded. Typically such current overloads result from voltage surges caused by lightning striking the structure in which these appliances are housed, or by striking an exposed power line. For such loads which are not individually fused, adequate protection may be obtained by the use of an electric cord equipped, as contemplated by the present invention, with its own individual circuit interrupter.
It should be understood that the term "circuit interrupter" is used to designate any device which provides a conductive link in an electrical circuit designed to "open" under overload thus interrupting the circuit. While various types of circuit interrupters are available, the type used in the present invention is restorable (or resettable) to the "closed" position thus reconstituting the circuit when the overload has been removed or cured. This type of circuit interrupter is generally identified as a circuit breaker whereas the common non-resettable type is known as a fuse which burns out or "blows" under overload.
The use of power cables which are "fused" as distinguished from those equipped with circuit breakers is not new; there being much prior art relating thereto. These suffer, however, from one major disadvantage, amongst others, in that the lack of a replacement fuse or the proper repair materials in an emergency may prompt someone to resort to evasive means for restoring a power cable to functionality, thereby, depriving its associated load of essential protection more or less permanently. This is because it is a common human tendency to leave an emergency repair as a permanent repair, thereby, totally defeating the intent and primary function of the fused power cable.
A variety of devices are known for isolating electrical appliances and the like from electrical currents in excess of a predetermined value. U.S. Pat. No. 4,307,925 discloses a male plug connector encapsulating a circuit breaker. In one embodiment, the reset button for the circuit breaker is located in the same surface as the terminals of the plug. In another embodiment, FIG. 5, the terminals extend radially outwardly from the longitudinal axis of the plug and the circuit breaker reset button is located in the surface from which the terminals would normally extend
U.S. Pat. No. 3,539,961 discloses an isolator having a male plug and a female receptacle connected together by a fusible link for insertion between an electrical appliance power line and a wall receptacle.